Asphaltenes are constituents of crude oils. They comprise a large number of structures, in particular high molecular weight fused aromatic components with heteroatoms. In view of the complexity of their chemistry, asphaltenes are described as the oil fraction which is soluble in benzene but not in n-pentane.
In crude oil, asphaltenes are usually present as a colloidal dispersion. This is stabilized by oil resins.
Asphaltenes can precipitate out during production, refining, transportation and storage of crude oil and products derived therefrom, such as, for example, heavy heating oil or marine oil. Common causes of this precipitation are a reduction in the temperature or a change in the composition (for example evaporation of readily volatile constituents). Asphaltenes can also precipitate out on flowing through porous media. Flooding with CO.sub.2 during the extraction process can make asphaltenes flocculate or precipitate out.
Some oils comprise hydrocarbon waxes which precipitate out at low temperatures. Interactions between the precipitating out of wax and asphaltenes can increase the total amount of substance precipitated out or the rate of formation thereof.
Asphaltenes which have precipitated out cause problems during production and during processing of crude oils. Asphaltenes are precipitated in valves, pipes and conveying devices. On hot surfaces, such as, for example, heat exchangers, carbonization of these precipitates can make their removal very difficult. The precipitates reduce the efficiency of plants and in the worst case can lead to a complete blockage and to a stop in production, which results in high costs.
Heavy oils, which are often used for powering ships, comprise considerable amounts of asphaltenes. Precipitating out of asphaltenes can lead both to poor combustion and to difficulties during handling and storage of the fuel. Combustion disturbances due to precipitating out of asphaltenes are also observed in power stations operated with heavy oils.
Bitumen, heavy oils and residues are sometimes diluted with solvents to reduce the viscosity for transportation. If asphaltenes precipitate out here, then there are problems during handling.
Precipitating out of asphaltenes can be prevented or reduced by small amounts of dispersing agents. These substances show one or more of the following effects:
a) the amount of precipitate is reduced; PA0 b) the precipitate forms more slowly; PA0 c) the precipitate is more finely divided; and PA0 d) the tendency of the precipitate to be deposited on surfaces is reduced. PA0 a) alkylphenol-formaldehyde resins PA0 b) oxalkylated amines, PA0 c) alkylbenzenesulfonic acids, PA0 d) wax-dispersing agents.
If precipitates of asphaltenes have already formed, they can be removed by using solvents. The addition of a dispersing agent can improve the effectiveness of these solvents.
A large number of asphaltene-dispersing agents are already known. CA 2 029 465 and CA 2 075 749 describe alkylphenol-formaldehyde resins in combination with hydrophilic-lipophilic vinyl polymers. The asphaltene-dispersing properties of dodecylbenzenesulfonic acid have been described in U.S. Pat. No. 4,414,035, and also by D. -L. Chang and H. S. Fogler (SPE paper No. 25185, 1993) and by M. N. Bouts et al. (J. pet. Technol. 47, 782-7, 1995). Oxalkylated amines are described in U.S. Pat. No. 5,421,993.
The dispersing agents known to date can only partly solve the problems caused by precipitating out of asphaltenes. Since oils vary in their composition, individual dispersing agents can operate effectively only in a limited range. Sometimes even small changes in the oil composition have a major effect on the dispersing properties for asphaltenes. In some cases, the known dispersing agents are therefore not satisfactory and additional types are necessary.
There was therefore the object of providing novel asphaltene-dispersing agents which do not have the disadvantages described for the dispersing agents known to date.